Centred text is hard to read.
I think many website developers centre text because it makes it easier for the website to work on different devices. When you increase or reduce the size of the screen, centred text stays roughly in the same place, in the middle. The page looks tidy, but if your words are important you’re not making them easy to read.
In my book, Writing for the Web, I explained that centred text creates work for the reader. His or her eye has to find the beginnings and ends of lines in different places.
For short headings or statements, it’s not a problem. On a traditional copper-plate invitation card it’s not a problem either, because each line contains a specific bit of information relevant to the event, and the recipient has time to study it.
But users of your website don’t have time to study what you want to tell them: why should they make the effort? I quite often skip the slabs of centred text on the home pages of websites and move with relief to pages that are better laid out, with lines of text that start in the same place on the left.
Here’s an example from a home page:
Here’s the same text on a slightly smaller screen:
I know which I find easier to read.